Portable devices are known which employ global positioning system (GPS) based position information such as handheld telephones, personal digital assistants, internet appliances, and other portable devices. Such devices typically employ multi-band wireless communication to allow the device not only to receive GPS information, but also communicate via one or more other wireless communication networks such as wireless cellular networks, short range wireless networks, and other networks. It has become increasingly important to be able to accurately locate the device for emergency purposes in the event the user of the device needs emergency assistance. However, satellite network based positioning signal systems are line-of-sight systems and therefore GPS antenna performance degradation can occur due to a user's physical interactions with the handheld device in such ways that can block or significantly degrade the GPS antenna performance (e.g. holding a device sideways).
Global positioning system receivers may be formed integrally with personal computers, portable telephones and other devices. Such devices include GPS signal processing circuits that decode received signals and carry out the arithmetic operation for calculating position information. Alternatively, a device may receive the GPS measurements and send them to an off-site element, such as a network element available in a wireless network which then carries out the arithmetic computations and sends back the latitude and longitude information to the device or other network element.
Some GPS reception systems have been proposed in which a device employs a built-in antenna and an external antenna and the receiving antenna is switched from the built-in antenna to an external antenna. Such an external antenna may be used when a sufficient reception level for positioning can not be obtained using only the built-in antenna. Such proposed devices typically require the use of an external removable antenna which require a user to carry an antenna with them and plug it into the housing when desired.
In addition, in order to choose the appropriate antenna, the system specifies a number of GPS satellites from which to take measurements and then from the extracted specified number of satellites, the antenna switching control unit designates the antenna with the high reception levels detected from the fixed number of satellites. However, such devices may not maximize the GPS position resolution capabilities of the device since the antenna with the strongest signals is typically chosen regardless of whether an antenna can be used to detect more satellites than the other antenna.